Underground pipes that are buried in the ground and used for sewers and the like can cause environmental problems such as caving of roads or leakage of sewage due to cavities in the ground surrounding the underground pipe that occurred when the pipe was buried and cracks or fractures in the underground pipe that appeared thereafter. The state of the underground pipe lines has to be inspected to prevent such problems effectively. Devices designed to be employed for such an inspection have been suggested and used. A cavity inspection device using a pipe line internal self-propelled vehicle that is equipped with a radar is described in Japanese Patent Application Laid-open No. H10-2969 as a device for examining cavities present in the ground around an underground pipe from inside the pipe line of the underground pipe. Further, a device for taking pictures of the inner peripheral surface of a pipe line, which used a pipe line internal self-propelled vehicle carrying a camera, has been used as a device for examining cracks or fractures in the underground pipe after it has been buried, the examination being conducted from inside the pipe line of the underground pipe.
However, in the aforementioned cavity inspection device, the radar search is conducted only upward of the underground pipe and search toward both sides and downward of the underground pipe is not an object. However, a search conducted only upward of the underground pipe is insufficient for preventing caving of roads, and a search toward both sides and downward of the underground pipe is also necessary. Furthermore, in the device for taking pictures of the inner peripheral surface of a pipe line, the camera is usually fixed in the forward direction or rotated along the inner peripheral surface. However, when the camera is fixed, a detailed image is difficult to obtain, and rotating the camera requires a complex mechanism. Further, devices designed to display cracks or pattern of irregularities on the inner peripheral surface of a pipe line with a three-dimensional convergence image have not been found.
In concrete underground sewers, hydrogen sulfide contained in sewage is converted into sulfuric acid by sulfur oxidizing bacteria, and this sulfuric acid reacts with cement components contained in the concrete and is converted into gypsum dehydrate, thereby causing concrete embrittlement. The embrittled portions have to be removed, for which purpose the concrete of the inner peripheral surface of the sewer has to be sampled and analyzed, this operation being costly and troublesome. Moreover, the analysis requires about 10 days.
Further, because the cavity inspection device using a pipe line internal self-propelled vehicle has a large size, inspection of underground pipes of small diameter, such as lateral sewers connected from the ground surface to the main sewer pipe, is difficult to conduct by employing such a large cavity inspection devices using a pipe line internal self-propelled vehicle.
With the foregoing in view, it is an object of the present invention to provide a device for inspecting the inside of an underground pipe line that makes it possible to search for cavities on the outside of the underground pipe over the entire internal peripheral surface of the underground pipe, that is, not only upward of the underground pipe, but also toward both sides and downward thereof, to obtain detailed images of the inner peripheral surface of the pipe line, without using a complex mechanism, and to display patterns of cracks and irregularities on the inner peripheral surface of the underground pipe by three-dimensional convergence images. Another object is to provide a device for inspecting the inside of an underground pipe line that can easily judge the presence or absence of concrete deterioration inside underground sewers made from concrete and a method therefor. Yet another object is to provide a device for inspecting the inside of an underground pipe line that can be used for inspecting underground pipes of a small diameter, such as lateral sewers, which are connected from the ground surface to the main sewer pipe, and an inspection method using such device.